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Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Nuova fisica nel settore del top ad LHC Leonardo Benucci, INFN Pisa e Università degli Studi di Pisa (the first and the last slide in Italian!)

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Top quark: what is it? large mass: m t ~ 170 GeV ~ 35 m b ~ EW scale Yukawa coupling close to one: t = √2 m t / v ~ 0.98 t = √2 m t / v ~ 0.98 Are them only accidents? Is the top mass generated by a standard Higgs mechanism? …maybe it plays a more fundamental role in EWSB? Playing with LHC, we hope to approach the answers…

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Top quark: why we like it? t quark production and decays are evaluated within the Standard Model with high accuracy without any phenomenological parameters t quark decays through the ONLY channel t bW. Other decay channels have BR<10 -3 (t) ~5 10 -25 s, QCD ~10 -24 s: no formation of top-hadrons Any experimental observation of unusual process with top is an indication of a New Physics Top quark is a laboratory where unique and powerful instrument can be found: to test precisely the Standard Model to look beyond it

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 LHC: a top factory LHC CMS ATLAS ~87 % 10 t t pairs per day @ Tevatron 1 t t pair per second @ LHC qq → t t : 85% gg → t t : 87% NLO cross-section NLO = 833 pb ~8M events/10fb -1 ~3.7M events/10fb -1 NLO = 153+90 pb NLO = 6.6+4.1 pb NLO = 30+30 pb

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 The birth of a top Production cross section: exotic production mechanisms predicted by several models Flavour changing neutral couplings SUSY charged Higgs: H ± t b SUSY top : t ~ t t t +X, t t t ~ t +X… Topcolor-assisted technicolor, Extra EW gauge bosons...: - there are heavy Z'and W' coupling preferentially to the third generation - there are heavy Z'and W' coupling preferentially to the third generation - there are t’ fermions decaying t’ Wb top-pions (t t, t b,...) bound by the strong topcolor dynamics (visible in single top production) (hep-ph/9911288) q, g t tttt t X t t pair production single-top production

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 The birth of a top q, g t tttt t X t t pair production single-top production Resonant production: Heavy new particles decays X t t and enters here Topcolor : there is a new strong gauge force coupling preferentially to the third generation a t t condensate is formed Top Spin Polarization: The SM predicts how t and t spin are correlated right-handed weak interactions or production via intermediate scalar may cause a deviation from SM These processe affect both QCD and EW production

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Resonant production Search for resonances in the t t mass spectrum d (t t)/dm(t t) ATLAS (ATL-PHYS-PUB-2006-033): Which is the minimum (x BR) prod. cross-section to discover X at 5 ? Which is the minimum (x BR) prod. cross-section to discover X at 5 ? It depends from M X and from ∫ L No narrow X(t t ) resonance was found at Tevatron: CDF: M X < 725 GeV, DØ: M X < 680 GeV CDF conference note 8087 (2006) DØ conference note 4880 (2005) with more than 10 signal evs. “where no man has never gone before”… other distr. addressable with high statistic: d /d , d /dp T in pair or single prod. sensitive to New Phys.

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Production cross section: top pair Measure of (t t) are becoming better and better... The future: CMS 10 fb -1 (similar results for ATLAS ): semilept: (t t)/ (t t) = 0.4%(stat) ±9.7%(syst) ± 3%(lum) systematic uncertainties in the btag eff( 5%) 7%, PDF 3.4%, pileup 3.2% di-lept: (t t)/ (t t) = 0.9%(stat) ±11%(syst) ± 3%(lum) fully had: (t t)/ (t t) = 3%(stat) ±20%(syst) ± 3%(lum) The present: no claims for deviations @Tevatron: DØ combined 7.1 +1.9 -1.7 pb CDF combined 7.3±0.9 pb Theo expect.(√s = 1.96 TeV, m t =175 GeV): 5.8 - 7.4 pb Tevatron with 10 fb -1 : (t t)/ (t t) <6%

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Production cross section: single top The present: DØ: single top events with 3.4s have been observed with cross-section exceeding SM (hep- ex/0612052) CDF, different results: s+t < 2.6 pb 95% (CDF Note 8677), s+t < 3.4 pb 95% (CDF Note 8185) 3 different (correlated) extraction techniques Inclusive (t channel + s channel) analysis Much more statistic is needed to draw significant conclusion LHC is expected to provide an indipendent estimate

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Production cross section: single top t-ch: / = 3%(stat) ± 7%(syst) ± 5%(lumi) (10 fb -1 ) ( hep-ph/0408049) s-ch: / = 18%(stat) ± 31%(syst) ± 5%(lumi) (10 fb -1 ) ( CMS note 2006/084) Wt-ch: / = 6%(stat) ± 16%(syst) ±5%(lumi) (10 fb -1 ) ( CMS note 2006/086) Fight with system. from: detector: JES at high eta,ISR+FSR for jet veto, b eff theory: PDF, QCD scale, m t The future: much larger statistic, much better S/B The future: much larger statistic, much better S/B

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Spin of top and spin of antitop How LHC can look at top spin? no t hadronization spin is transferred to decay products choose the helicity base: t and t flight direction count production rates of like-spin and unlike-spin pairs evaluate A: The SM says: when produced by gg: 3S 1 state ( ) when produced by qq: 3S 0 state ( ) (close to production threshold) An excess of spin point in the same direction is expected: The problem is: what can we choose as 'spin analyzer'? t is correlated with its decay products: (l,d)=+1, ( )=-0.31, (W)=0.41, (u,b)=-0.41 So looking at the l from W is the best choice: LHC will deliver ~400 kevs dilept after 10 fb -1 : angle between the decay products of t and t in the respective rest frame

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Di-lepton channel: spin analyzers are both l W t Lepton+jets channel: spin analyzers are l W t and d W t (~100% polarized wrt the t spin) pratically: the least energetic jet in the t ( t) rest frame (only 51% polarization) Spin of top and spin of antitop 1 ( 1 ): angle between the spin analyzers of t (t) in the t ( t) rest frame and the t( t) direction in the t t frame 1 ( 1 ): angle between the spin analyzers of t (t) in the t ( t) rest frame and the t( t) direction in the t t frame FIT THIS DISTRIBUTION AND FIND A Single top can be addressed to search spin correlation: Single top can be addressed to search spin correlation: top is highly polarized in some bases (‘spectator’ jet can be chosen) very large statistic CMS(30 fb -1 ) : CMS(30 fb -1 ) : A = 0.346 ± 0021(stat) +0.026 -0.055 (syst) (quite similar for ATLAS) Tevatron, Tevatron, poor limits: A > -0.25 (at 68%CL) (A exp ~ 0.9)

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 The top during its life Top Mass: is an important input in the SM is an important input into theories for BSM (key role in the MSSM, and inspires theories such as top color) Constraint on h mass: m h < 130 GeV with current m t values Top charge: Are we looking to an exotic Q=4/3 particle? (t W + b) Tevatron Run-II has enough statistic to rule it out: Q=2/3 at 94% C.L. (DØ conference note 4876, 2005) Top Width: (t)/|V tb | 2 =1.42 GeV : the total not measured yet! = 1/ ~5 10 -24 s c ~3 10 -10 µm Additional quark generations, non-standard top quark decays or other SM extensions could yield long-lived top quarks in the data CDF: measurement of distance between primary vertex and leptonic W ± decay vertex in lept+jets events c < 52.5 µm is found at 95% CL (CDF conference note 8104,2006) t X

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Top is becoming thin... Radiative corrections to many precision EW observables are ~m t 2 Meas. M W and m t + SM predictions test the consistency of the SM or point to SUSY Better and better at Tevatron: End of Run-I: 178.0 ± 4.3 GeV Preliminary data from Run-II: 172.5 ± 1.3(stat) ± 1.9(syst) GeV March 2007: 170.9 ± 1.1(stat) ± 1.5(syst) GeV From a EW fit (~indipendent from m t meas.): m t = 172.3 +10.2 -7.6 GeV (PDG’06)

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 The future of top mass (1.5%) (2%) (5% On-Off) LHC: Tevatron performances should be reached and improved Di-lepton channel: m t / m t = 0.5 (stat)± 1.1 (syst) GeV @10 fb -1 Lepton+jet channel: m t / m t = 0.3 (stat)± 1.1 (syst) GeV @10 fb -1 (ATLAS hep-ex/0403021, CMS TDR 8.2, CERN/LHCC 2006-021) With a good systematics control ( bJES<1%, btag eff.<2%, accounting for FSR…) ( m t / m t ) TOT ~1 GeV is at hand

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 The death of a top The focus is on the tWb vertex: The SM says: tWb coupling is purely left-handed at tree level (V-A) its size is given by the CKM matrix element |V tb | flavour changing neutral (FCN) couplings are forbidden at tree level New anomalous couplings (e.g. new radiative contributions) can appear already at tree level and modify the structure of the tWb vertex A window to a new world is open: SM Higgs, MSSM, s- fermion, SUSY with R violation… CP Violation: very small effects in SM and in BSM (maybe some chances at ∫ L > 150 fb -1 ) t b (q…) W (V…)

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 W boson: how does it spin around? The V-A interaction controls the helicity fractions of the W W is produced with different helicity fractions: longitudinal F 0 = 0.703 left-handed F L = 0.297 right-handed F R = 3.6 10 -4 (SM at tree level,m t = 175 GeV, M W = 80.39 GeV m b = 4.8 GeV) How to measure them? look at the W l decays measure the angle between the l in the W rest frame and the W in the t rest frame extract F fractions from FLFLFLFL F0F0F0F0 FRFRFRFR

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 W boson: how does it spin around? Tevatron: Because of lack of statistic, M(lb) (related to cos ) and p T (l) (related to polarization) better suited CDF: F 0 = 0.74 +0.22 -0.34, F R < 0.18 95% C.L MC generator level CMS reconstruction level (full sim): - there is the background - there are detector effects CMS 10 fb -1 : F 0 /F 0 = 0.023 (stat) ±0.022 (syst) significant impact of systematics: b-jet energy scale b-tag efficiency input m t ISR/FSR

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 tWb: not only W helicity… Other variables (less prone to systematics) can be looked at: F L,R /F 0 ratios top angular asymmetries, e.g.: Nice systematic effects reduction is obtained (ATL-PHYS-PUB-2006-031) Then the observables can be used to constrain the couplings in the general Lagrangian: -0.0566

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 |V tb |: a window to New Physics If |V tb | < |V tb | CKM ~ 0.9991 : t XW would be possible (4th generation of quarks or other...) (4th generation of quarks or other...) The number of events with 0, 1 and 2 tagged b-jets is compared (in di-lepton and lept+jets) to extract the ratio: R(2b/≥1b) = BR(t Wb)/ ( BR(t Wd) + BR(t Ws) + BR(t Wb) ) = |V tb | 2 / ( |V td | 2 + |V ts | 2 + |V tb | 2 ) = |V tb | 2 assuming only 3 generations and CKM unitarity LHC with the same technique: R/R ~ 0.2%(stat) @ 10 fb -1 |V tb |/|V tb | ~ 0.1% (Systematic: b-tagging uncert. ) At Tevatron: DØ: R = 1.03 +0.19 -0.17, R > 0.64 CDF: R (stat) = 0.94 +0.21 -0.19 (stat) +0.17 -0.13 (stat), R > 0.61 |V tb | > 0.78 (0.75) at 90% (95%) CL |V tb |/|V tb | ~ 5% at Run IIb

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 At Tevatron: DØ: |V tb | estimated in the first single-top observation: |V tb | = 1.00 +0.00 -0.12 EW (t) |V tb | 2 |V tb | can be extracted directly: no assumption is needed on the number of families or CKM unitarity |V tb |: the promises of single-top LHC (t-channel): EW (t) / EW (t) ~ 10% |V tb |/|V tb | ~ 5% @30 fb -1 tt’ pair Single-t’ t-ch Single-t’ s-ch Single-t’ Wt-ch If not observed: maybe t-t’ mixing? (hep-ph/0607115)

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 FCNC: a signature of new physics At LHC, FCNC Br might reach a detectable level ANY OBSERVATION AT LHC WILL BE A SIGNAL OF NEW PHYSICS FCNC decay Br in SM t q 5 10 -13 t Zq 1.3 10 -13 t g q 5 10 -11 Br in SUSY + R violation ~10 -5 ~10 -4 ~10 -3 Br in 2HDM ~10 -7 ~10 -6 ~10 -4 LR - SUSY ~10 -6 ~10 -4 ~10 -3 Exp. Limits (95% CL) < 0.006(HERA) < 0.14(LEP2) < 0.17(CDF) t b W Today we only see: t W b (Br > 99.9%) Tomorrow we could see: t Aq (Br =??) where q = u, c, A= Z, g, t q A NP g single top production tZ/ production tt like-sign production ,Z top decay in t t events

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 FCNC: a signature of new physics ATLAS + CMS @ 10 fb -1 /exp t qZ: 2.1 10 -4 t q 6.2 10 -5 ATLAS + CMS @ 100 fb -1 /exp t qZ: 4.7 10 -5 t q 1.7 10 -5 + WITHOUT SYST. WITH SYST. further constraints may come from qq’ tZ/ and single-top t-ch

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 When a top meets a Higgs... tH Yukawa coupling is strong: tH Yukawa coupling is strong: if the Higgs exists, qq’ tt H will be visible t t pair could provide the Higgs discovery! Best way to search for it: fully reconstruct the tt pair search for a large BR Higgs decay (H b b, t t) ATL-PHYS-2004-031, CMS NOTE 2003/03 In light SUSY scenario: t H + b (large when tan » 6 or tan « 6) tan ß«6: H , tan » 6: H cs LHC: R(2l/1l) = BR(dilept)/BR(lept+jets) = BR(W e/ )/2BR(W had) ~ 1/6 LHC: R/R ~ 0.5%( stat) @ 10 fb -1 Tevatron: Selection criteria are optimized for standard decays, H decays has no energetic isolated leptons t “disappearance” in lept+jets BR(t H ± b) < 0.4 (if only H is present) BR(t H ± b) < 0.91 (model independent) q, g t tttt H y t t SM Higgs SM Higgs SUSY Higgs SUSY Higgs

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 The promises of LHC Tevatron today LHC LHC > 100 fb -1 (t t) 12%<7-8%<7-8% EW (t) 30% < 9-10% < 7-8% m t (GeV) 1.5 ~ 1.0-1.2 ~1.0-1.2 A/A (spin correlation) ≈50%<7-8%<5-6% |V tb | (direct meas.) 15%<4-5%<3-4% BR(t Zq) (CDF 2 fb -1 ) 2 10 -3 5 10 -4 1 10 -4 BR(t q) (CDF 2 fb -1 ) 3 10 -3 1 10 -4 4 10 -5 When at LHC (ATLAS and CMS) we will have: negligible statistic uncertainty (10-30 fb -1 ) most of systematics under control we expect: (in a nutshell) …further improvements when ATLAS and CMS will be combined together!

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Conclusion: looking forward to produce many top… LHC will open an entirely new era of top physics... to do much better measures of the known... to start elucidating the unknown precise m t measures will constrain the Higgs and enter the SUSY world cross-section and spin correlation in t t examine the QCD production the secrets of single-top: precise |V tb |, hints of W', H ±, FCNC sensitivity to anomalous coupling is good and points directly to New Physics

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 …to shed light on Physics misteries QCD Electroweak physics Higgs or new physics We know there is new Physics at the electroweak scale t We really don’t know what it is Top quark is the THE key to enter this physics

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Production cross section: single top …The ratio s (W tb)/s (W ) could be sensitive to W H bosons up to 1.5 TeV: …How far is new physics?

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007 Three top quark mass estimators are investigated: 1. Gaussian fit on reconstructed mass spectrum → m t Simple 2. convolution with Gaussian parametrized ideogram → m t ParamIdeo 3. convolution with full scanned ideogram → m t FullIdeo A likelihood variable is constructed reflecting the probability for signal → P sign Jet combinations are ordered according to a likelihood variable → P comb A kinematic fit is applied ( CMS Note 2006/023 ) forcing the W boson mass The Ideogram is convoluted with a theoretical template Maximum likelihood gives the estimated top quark mass 4 th estimator: m t FullIdeo but IterCone, MidPoint & k T should give same jet direction Breit-Wigner Monte Carlo parametrized can be fixed in kinematic fit

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1 Leonardo Benucci, Nuova fisica nel settore del top ad LHC – IFAE Napoli 11-13 Aprile 2007

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